1. Field of the Invention
The present invention relates to an alignment measuring apparatus for an automotive vehicle wheel in which the inclination angles, including the toe-in angle and the camber, of a wheel mounted through the suspension of a vehicle are measured using a non-contact measuring technique by optical length measurement with the wheel rotating and stationary.
The inclination angles used for indicating the mounting position of the wheels of an automotive vehicle or the like include the inclination angle of the wheel or the tire surface with respect to the direction of progress of the vehicle (toe-in angle), the degree of inclination of the wheel or the tire surface with respect to the vertical plane (camber angle), and the caster. Accurate measurement and adjustment of the wheel alignment including all of these angles is an important factor for improving the driving characteristics.
In this specification, the xe2x80x9cwheelxe2x80x9d is defined to include the tire portion and the rim flange of the. wheel.
The toe-in angle is an angle indicating whether the tires are wider apart at the front or at the back as viewed from above the vehicle body and concerns both the front and rear wheels. If wheels are wider apart at the front, this is called toe-out, and if the wheels are wider apart at the rear, this is called toe-in.
The camber angle is an angle indicating whether the wheel is wider apart at the top or at the bottom as viewed from the direct front or rear of the vehicle, and represents the angle formed by the normal to the ground contact point of the tire and a straight line along the tire. When the tire is perpendicular to the ground, the camber is zero; when the tire is inclined inward, the camber is negative; and the tire inclined outward is positive in camber. The camber angle is measured for the purpose of facilitating the steering operation, reducing the vertical load and preventing the wheel from becoming wider apart at the bottom.
The caster, which is required for maintaining the straight-line stability, is defined as the angle between the vertical at the wheel center and the inclination of the king pin shaft as viewed directly sideways from the wheel. A positive caster is involved if the king pin shaft is inclined rearward, a negative caster is involved if the king pin shaft is inclined forward, and a zero caster is involved if the king pin shaft is in a vertical position.
2. Description of the Related Art
As a conventional alignment measuring apparatus, a direct contact measuring apparatus for measuring the angle by bringing the measuring unit into direct contact with the tire disclosed in Japanese Examined Patent Publication (KOKOKU) No. 62-121128 is known.
In recent years, as disclosed in Japanese Unexamined Patent Publication (KOKAI) No. 7-081853, a non-contact wheel alignment measuring apparatus, using optical length measurement, free of mechanical wear or degeneration which imposes no stress on the object of measurement has been realized in place of the wheel alignment measuring apparatus of contact type. The newly-developed apparatus uses a light beam based on trigonometry.
A method of measuring the wheel alignment statically by optical length measurement without using the light beam for trigonometry is the method disclosed in Japanese Examined Patent Publication (KOKOKU) No. 6-025661. In this method, a point corresponding to a reflected image of a slit light is determined by one camera, and the position of the corresponding point is calculated by another camera using the geometric restraints of the slit light. For this reason, a vast amount of calculations is required between the image data of the two cameras. Therefore, the application of this method to the dynamic in-line wheel alignment measurement requiring the high-speed determination of the inclination angle is very difficult, and practically limited to static wheel alignment measurement. In the measurement and adjustment of the wheel alignment of the vehicle with the wheels mounted, the wobbling of the wheel rim is a major cause of an error. Currently, therefore, the dynamic wheel alignment measurement is essential in which the wobbling of the wheels or the rim is corrected. With the method disclosed in Japanese Examined Patent Publication (KOKOKU) No. 6-025661, however, accurate dynamic wheel alignment measurement is difficult.
Among the apparatuses for non-contact measurement of the wheel alignment of a vehicle while rotating the wheels of the vehicle, the techniques disclosed in Japanese Examined Patent Publication (KOKOKU) No. 6-011420 and Japanese Unexamined Patent Publication (KOKAI) No. 9-329433 concern a method using a spot laser displacement meter based on triangulation. In the method disclosed in KOKOKU No. 6-011420, however, the distance measuring sensor is the spot laser displacement meter, and therefore, as the conditions. for accurate measurement, the tire side profile is required to be exactly symmetrically homogeneous diametrically about the wheel center around the whole wheel. Actually, however, the tire side section has a complicated shape, has an unevenness due to letters or the like and it is not symmetrically homogeneous. Further, unless a pair of distance measuring sensors and the swivel axes thereof are arranged equidistantly coaxially with the center of the wheel involved, the radiation point of the laser spot is deviated and constitutes a cause of a serious error. Taking into account the behavior of the vehicle while the wheels are rotating at the time of measuring the manufacturing variations of the wheel base of the vehicle, however, accurate positioning is very difficult and a high-accuracy wheel alignment measurement is impossible. In the method disclosed in KOKAI No. 9-329433, on the other hand, the distance measuring sensor is mechanically scanned, and therefore, the scanning mechanism is worn or unavoidably deteriorated on the one hand, and a considerable time is required for determining the number of measuring points required for correcting the wheel frame. The higher the measuring speed, the earlier the wear or deterioration occurs, leading to the disadvantages of a reduced accuracy and a higher maintenance cost.
Among the apparatuses for measuring the wheel alignment of the vehicle in non-contact fashion while rotating the wheels, the technique disclosed in KOKOKU No. 7-081853 is a method using a two-dimensional laser displacement meter based on triangulation. This method, in spite of its advantage of compensating for the disadvantage of the spot laser method described above, has the disadvantage that the laser projection width and pattern are fixed so that the portions requiring no measurement are also exposed to the light, and irregular reflection occurs for some objects of measurement due to the difference in the edge shape or the material. In these methods using the two-dimensional area photo detector, a screen (or field) is instantaneously exposed to light, and therefore, in the worst case, the irregular reflection may have an adverse effect even on the portions which would have otherwise been normally measured. Such adverse effect is very difficult to identify and remove, thus often resulting in a considerable measurement error or making the measurement impossible.
In the situation requiring a rotational angle of the wheel of at least 10xc2x0 when measuring the steering angle or the caster by turning the steering wheel using the conventional method in which the angle detection mechanism is brought into contact with the tire side surface, it is difficult for the detection mechanism to track and detect the tire side uniformly following the wheel center. This causes a measurement error of the toe and the camber, thereby making it impossible to measure the steering angle and the caster with high accuracy. Even in the conventional non-contact measuring apparatus, the detection point defining the tire side is a specific spot on the tire side wall or a point nearest to the tire side wall from the detector, so that the steering angle cannot be measured or the measurement error of the toe and camber is so excessive that high-accuracy caster measurement is impossible.
In all the methods of the prior art, the laser projection width and the pattern are fixed. Therefore, in the case where the vehicle tire and the peripheral parts thereof which have a complicated shape is the object of measurement, light is radiated also on the portions requiring no measurement, and irregular reflection occurs depending on the edge geometry, gloss or material. As a-result, in the worst case, even the portions which could otherwise have been normally measured are adversely affected, often causing a considerable measurement error or even making the measurement impossible. To cope with this problem, the conventional apparatus sometimes comprises software means for processing only the required portion of the brightness information read by the light-receiving side or removing faulty points by arithmetic operation. This cannot provide means for suppressing the cause of the disturbances in the projection stage which is a source of the irregular reflection. In the active sensor for applying light to these objects of measurement, the performance and operability can be further improved by appropriately designing the projection method.
In the method using the spot laser displacement meter, on the other hand, accurate positioning of the sensor is difficult with respect to the wheel rotational shaft center, and therefore the sensor is mechanically scanned. It is difficult, however, to maintain an accurate sensor position for a long time due to the mechanical wear and tear. The situation may become more difficult if the projection width and the pattern is to be made variable, as a more complicated mechanism is required.
The optical cutting method which uses trigonometry requires an accurate arrangement of the laser projection angle and position with respect to the tire, the direction of camera detection and position, thereby leading to the shortcoming of complicating the mounting jigs while at the same time requiring labor-consuming installation, adjustment and calibration.
Thus, an alignment measuring apparatus, which can handle a variety of objects in-line and measure and adjust the dynamic wheel alignment with high accuracy free of maintenance for a long period of time, is in demand.
The object of the present invention is to provide a simple, inexpensive vehicle wheel alignment measuring apparatus in which the radiation range for a great variety of wheels constituting objects of wheel alignment measurement can be dynamically changed at high speed and in versatile way at many points of the required portions alone and, at the time of projection, the radiation range is specified to be unaffected by disturbances such as irregular reflection, while at the same time reading the brightness information on the photodetection side in collaboration and synchronism with the limitation of the radiation range, so that only the target radiation range within the measurement area can be processed with high speed, thereby obviating the disadvantage of the prior art described above and making it possible to measure the dynamic characteristics of the wheel alignment with high accuracy.
In order to achieve the aforementioned object, according to a first aspect of the invention, there is provided a vehicle wheel alignment measuring apparatus for measuring, in non-contact fashion, the wheel alignment of a vehicle on rotating wheels, comprising laser light source means for radiating a laser beam having a section of a predetermined geometric pattern at least toward the side of a wheel, laser beam control means for controlling the laser beam in such a manner as to radiate the laser beam only within a predetermined range on the side surface of the wheel, a photodetecting device for receiving the laser beam reflected in a predetermined range on the side surface of the wheel under the control of the laser beam control means and converting the received laser beam into a corresponding image data, and processing means for calculating the wheel alignment by processing the image data.
In view of the fact that the laser beam from the laser light source means is radiated only in a predetermined range of the side surface of the wheel, disturbances such as irregular reflection can be suppressed in advance. Also, by processing only the required range within the visual field, the alignment can be measured at high speed with high accuracy as compared with the prior art.
A two-dimensional area photodetector is preferable as the photodetecting device.
Since the two-dimensional area photodetector is used, the intended range, i.e. the scanning range of the light source, even if dynamically changed as required within the preset range of the visual field, can be detected easily with a simple threshold-setting process, thereby permitting an alignment measurement at higher speed.
The one-dimensional line photodetector can also be used as the photodetecting device.
In the method using the one-dimensional line photodetector, the laser beam is received and processed sequentially by scanning the beam reflected from the geometric pattern in the one-dimensional direction, and therefore, even in case of a disturbance such as irregular reflection that may occur, the faulty data is localized at the particular time point, and the data that have been and will be normally retrieved are not affected. Also, the one-dimensional line photodetector is advantageous for obtaining a high resolution and can simplify the processing operation, and therefore can make possible the alignment measurement with lower cost and higher accuracy than the method using the two-dimensional area photodetector.
In the case where the one-dimensional line photodetector is used, however, the information indicating the horizontal-position along the scanning direction of the laser beam source is required from light source control means or another position detecting means.
According to a second aspect of the invention, there is provided a vehicle wheel alignment measuring apparatus for measuring, in non-contact fashion, the wheel alignment of the vehicle on rotating wheels, comprising two laser light sources for radiating unparallel laser beams having a section of a predetermined geometric pattern at a finite predetermined angle toward at least different points on the side of the wheel, a photodetecting device for receiving the laser beams reflected from the side surface of the wheel irradiated with the laser beams emitted from the two laser light sources and converting the received laser beams into corresponding two image data, and processing means for calculating the distance between the two images based on the two image data and calculating the wheel alignment based on the calculated distance.
The two images formed on the side surface of the tire or the wheel by the laser beams from the two laser light sources are converted into image data by the photodetecting device, and then processed by the processing means, as described above. By measuring the change of the distance between the two images in accordance with the rotation of the tire, it is possible to measure the inclination angle of the wheel.
The distance between the two images on the tire or the wheel is not dependent on the distance between the laser beam light source and the photodetecting device, and neither the laser beam radiated on the tire or the wheel nor the reflected beam proceeding toward the photodetecting device is required to be exactly orthogonal to the surface of the tire or wheel. Thus, the installation and calibration of the laser light. source and the photodetecting device are substantially free of the effect of the mounting error or the aged deterioration, thereby improving the operability.